1. Field of the Invention
This invention relates to a heat sink, in particular a diamond heat sink having a very high thermal property, used for radiation of semiconductor devices or compressors.
2. Description of the Prior Art
With the miniaturization and increase of processing speed of information processing systems, the processing capacity per unit area of a semiconductor device built-in such a system is rapidly increasing. The result is an increase of the quantity of heat per unit area generated in the semiconductor device, and the importance of maintaining the thermal property thereof has been observed with keen interest when designing a substrate to be mounted. Up to the present time, a number of combinations of alumina substrates and metallic heat sinks with fins have been used, but because of the low heat conductivity (0.29 W/cm.multidot.K) of alumina, a sufficient thermal property cannot be obtained, even in combination with the metallic heat sink.
Requirements for the thermal property of a package to be mounted by semiconductor devices have become more severe because of an increase of the heating value with the high effectiveness of the devices to be mounted. Thus, as a means for lowering the heat resistance of the package, for example, it has hitherto been known to employ a higher heat conductivity material or to improve convection heat conduction by formed air cooling, forced water cooling, etc.
As a heat sink material of a semiconductor device having a higher thermal property, it has been proposed to use diamond, cubic boron nitride (CBN), aluminum nitride, etc. However, these high heat conductivity materials have a problem that, though their heat conductivity is higher than that of alumina, etc., their production cost is higher. In particular, diamond is contemplated as a heat sink for semiconductors, since the gaseous phase synthesis technique has lately been developed and progressed, and a sheet-shaped heat sink with a large area can be obtained. However, diamond is much more expensive than the ordinary materials of the prior art and its high heat conductivity cannot effectively be utilized, since a fit-fitted diamond heat sink cannot be prepared and joint use of a metallic fin-fitted heat sink is required.
Ordinary materials used for the package, for example alumina, will surely meet with a problem regarding the thermal property thereof when a higher performance device is put to practical use in the near future. Namely, in the present package, there will arise a problem that the heat resistance thereof is so large that heat generation of the device itself cannot be radiated sufficiently, thus raising the temperature of the device and the device will fail to function normally. In order to solve this problem, it is effective to use a high heat conductivity material, as described above, and diamond having the highest heat conductivity of prevailing materials has been used as a semiconductor laser diode. At the present time, as a diamond for radiation, there are used natural single crystal diamond or artificial single crystal diamond prepared by a high pressure synthesis method and polycrystal prepared by a gaseous phase synthesis method. However, they generally are limited to plate-shaped crystals. However, the heat transferred by a heat sink should finally be discharged through a fluid such as air or cooling water, and a structure with a large radiation area, such as a fin-fitted heat sink, is preferable for improving the heat exchange function with such a fluid.